In roll stands, herein also designated roll changing devices, a continuous unrolling of an earlier reeled web of for instance newsprint, paperboard etc. is done to some type of converting machine for treatment of said web, for instance, a printing machine for production of printed matter, magazines etc. or, for instance, a folding machine or cutting machine for production of miscellaneous other paper products. Roll stands of the type specified above are known in different designs. It is typical that also the competitive alternatives generally are constructed with the same technical properties and capabilities. Consequently, the price is an important and growing factor for the customer.
It is therefore a desire to manufacture a roll stand that comprises the most essential properties that are requested for the known roll stands of today, but to a substantially lower production cost per produced unit.
All roll stands for continuous unrolling of a web, always comprise at least two roll holders, each for at least one roll of the web-like material in question. For instance, the roll holders consist of two or several pairs of roll holding arms, which are arranged at and around a mutual, turning axis in the roll stand. The material rolls can of course consist of other materials than paper, for instance plastic or foil, but however, they normally consist of paper rolls from which a running paper web is consequentially unrolled without breakage to the current converting machine. This is done by splicing the roll, which is being used up, to a new replacement roll by a so-called “flying splice”, which replacement roll is held in preparedness in one of the other pairs of roll holding arms. The implication of the phrase “flying splice” is that the splicing is usually done without reducing the web feeding speed, or at least that it is substantially maintained during the actual joining. Thereby it is achieved that no unwanted breakage of the current production of, for instance, printed matter, magazines etc. occurs. It is understood that it is utmost important that the two different webs are spliced to each other with a great precision, in particular as the webs already may be provided with print for production of different printed matter and ontop of which first print, another and additional second print is to be applied at exact locations, for instance in connection with writing addresses on therefore arranged address tags on printed matter.
One of the essential properties mentioned above, which a well-working roll stand must be able to handle, is that the roll holding arms of the roll stand must be able to perform four different types of adjustments in a simple and effective manner, simultaneously as the precision still becomes very exact for all these adjustments.
These are, for the first, a roll holder positioning, i.e. the mutual adjustment of the lateral position of each roll holding pair which must be done, in which each pair is to be seen as one unit, along the hub girder of the roll stand, i.e. the central hub girder, around which the first roll, which is rotatably held during unrolling, the or those, second, third etc., roll or rolls, which are intended for web splicing, are turned. When the rolls have the same width, said position is normally the same for all the arm pairs. (In this description, the unit mentioned above is designated “roll holder”.)
Secondly, a roll width adjustment, i.e. the adjustment of the relative positions of the roll holding arms to the size of the current roll type, which for the time being is to be handled in the roll stand, for instance, depending on if the roll consists of a half roll or a full roll.
Thirdly, the chucking movement, which is performed in order to get one gripper at each roll holding arm in each pair of roll holding arms to be, in an alternating mode, released out of, and thereafter re-inserted into, the sleeve of the roll in connection with each roll change between an emptied roll to a new full roll, and which is normally done during ongoing unrolling at another pair of roll holding arms.
And finally, a fourth and relatively modest movement for a precision adjustment of the lateral position of a roll in relation to another roll in conjunction with web splicing and/or for an exact positioning of the material web to a desired web direction during the present unrolling.
Known Technique
According to conventional engineering, at least two separate motor-driven units are used in order to achieve the two first movements and the two later ones. The roll holder positioning and the adjustment of the reel width are done by means of a first separate drive unit which enables a movement of the roll holding arms in each pair of roll holding arms along the hub girder, both together as one unit in connection with the roll holder positioning and alone in connection with the adjustment of the reel width, while an additional drive unit provides a movement of each chuck for the chucking movement in connection with the roll change and for the precise adjusting movement at roll changing and/or during the current operation. This is a very expensive and complicated solution, which, in addition to this, brings along certain control-engineering problems, since two movements must be superposed on each other. Therefore, an advanced control unit is needed, for instance comprising a computing unit.
Through the development of the roll stand which is partly described in the document WO 99/46518, came a roll stand out on the market for the first time, in which all the movements (1-4) mentioned above are being handled of one and the same motor/drive unit arranged at each pair of roll holding arms. This roll stand is constructed in order to allow the largest imaginable flexibility, so that almost all kinds of different roll sizes can be driven without being locked to some few given positions for each roll holder arm. This has shown to be a very appreciated solution, but it is expensive, among other things because of the fact that the machine demands a very expensive analogous adjusting device with a high resolution (AIHU) and an enhanced and expensive adjusting device in the form of a very long high precision ball screw (HPKS).